The conditions of partial or complete inactivation of polyphenol oxidase (PPO) in apple juice were studied by heat treatment at different temperatures and times, and the inhibitory effect of a simulation system similar to the natural pH value of fruit juice on the enzyme activity of treated fruit juice was investigated. The results showed that PPO could not be completely inactivated at 75℃ for 30s, but its activity was greatly damaged. Low pH value (3.8), which is close to the pH value of fruit juice itself, can well inhibit the PPO enzyme activity after treatment, which is the best treatment condition. The medicinal use of apples was recorded as early as the Tang Dynasty. Apples can not only benefit the heart, promote fluid production and quench thirst, but also have the functions of "moistening the lungs and pleasing the heart, promoting fluid production and appetizing, and sobering up". "An apple a day" is a well-known health slogan. Indeed, apples are rich in sugars, organic acids, cellulose, vitamins, minerals, polyphenols and flavonoids, and are called "all-round healthy fruits" by scientists.